1. Cells communicate with each other through direct contact between adjacent cells via structures like gap junctions, or through signaling molecules that bind to receptor proteins on target cells. 2. Signaling pathways involve a signal molecule binding to a receptor which then activates an intracellular response through enzyme cascades or second messengers like cyclic AMP or calcium ions. 3. This leads to responses in the target cell like changes in cellular activity, gene expression, or enzyme activity.

1. Cell Communication

6. Direct Communication: Surface Proteins - Yeast Cells

11. Signal Transduction Pathway

24. Enzyme Cascade